knocker in WordNet English dictionary

1. either of two soft fleshy milk-secreting glandular organs on the chest of a woman
   breast  bosom  knocker  boob  tit  titty 
   
2. one who disparages or belittles the worth of something
   detractor  disparager  depreciator  knocker 
   
3. a device (usually metal and ornamental) attached by a hinge to a door
   knocker  doorknocker  rapper 
   
4. a person who knocks (as seeking to gain admittance)
   "open the door and see who the knocker is"
   knocker 
   
5. (Yiddish) a big shot who knows it and acts that way; a boastful immoderate person
   knocker